Current measuring apparatus, test apparatus, and coaxial cable and assembled cable for the apparatuses

ABSTRACT

There is provided a current measuring apparatus for measuring current-under-measurement flowing between a first measuring terminal and a second measuring terminal, having a plurality of primary coils whose one end is electrically connected with the first measuring terminal and another end thereof is electrically connected with the second measuring terminal, a secondary coil that generates voltage representing the current-under-measurement corresponding to the current-under-measurement flowing through the plurality of primary coils and coaxial cables, each corresponding to the plurality of primary coils and having a signal line that connects one end of the primary coil with the first measuring terminal and a shield, and the coaxial cable has the signal line, an insulating layer for coating the signal line, first one of the shield having a tape-like conductor wound around the insulating layer and second one of the shield made of a conductor provided around the first shield.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation application of PCT/JP2004/013753 filed on Sep.21, 2004 which claims priority from a Japanese Patent Application(s) NO.2003-330732 filed on Sep. 22, 2003, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a current measuring apparatus and atest apparatus as well as to a coaxial cable and an assembled cable usedfor the apparatuses. More specifically, the invention relates to acurrent measuring apparatus having coils that generate voltagerepresenting current-under-measurement and to a low impedance coaxialcable and an assembled cable used for transmitting thecurrent-under-measurement from a current supply.

2. Related Art

Conventionally, there has been known a current measuring apparatus formeasuring electric current based on a magnetic field generated by thecurrent-under-measurement. For example, a current probe measureselectric current based on voltage generated in a secondary coil of atransformer corresponding to the current-under-measurement flowingthrough a primary coil thereof.

In case of measuring source current of an electronic device, a powerterminal of the electronic device is connected with a current measuringapparatus by a coaxial cable or the like to inputcurrent-under-measurement to the current measuring apparatus. Anobservation zone is determined by such factors as capacity, inductanceand characteristic impedance in such measurement.

Because the capacity of a supply line is unchangeable here, it isdesirable to reduce the inductance and the characteristic impedance inorder to widen the observation zone. As an example of such low impedancecoaxial cable, there has been disclosed one in which a conductivelaminate made of aluminum foil and others pasted on a film base materialmade of polyester or polyimide as its substrate is wound around an outerperiphery of a conductor while putting the aluminum foil on theconductor side and an insulation layer is provided further around theouter periphery of the laminate (Japanese Patent No. 1992-56408).

However, it has been difficult to measure the current at high precisionby the conventional current probe due to an influence of inductance ofthe line through which the current-under-measurement flows. Therefore,it has been also difficult to perform IDDT test at high precision intesting an electronic device for example. Still more, because theinductance increases in proportion to a square of a number of turns ofthe primary coil in the current probe, insertion impedance increases inmeasuring the current if the number of turns of the primary coil is 2 ormore. Therefore, it has been troublesome to provide the current probe inwhich the number of turns of the primary coil is 2 or more and tomeasure micro-current at high precision by such current probe.

It has been also known that the closer an outer diameter of a signalline (core line) to an outer diameter of an insulator provided aroundthe signal line, the smaller a value of characteristic impedance of acoaxial cable becomes. Here, the coaxial cable described above isarranged so as to bring an outer diameter of the signal line closer toan outer diameter of the insulator by increasing an effective sectionalarea and an effective radius of the conductor, i.e., the signal line, bymeans of a conductive laminator. However, the coaxial cable describedabove is intended for 50Ω or more of value of characteristic impedanceand cut-through resistance is increased by fully increasing a thicknessof the surrounding insulator.

Meanwhile, it is necessary to extremely thin the thickness of theinsulator to relatively reduce the outer diameter of the insulator inorder to realize a coaxial cable whose value of characteristic impedanceis several Ω for the purpose of measuring source current of anelectronic device. It is then necessary to facilitate uncovering of theinsulator by increasing the cut-through resistance and to satisfythreshold voltage of the insulator in the same time in order to realizeit.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a currentmeasuring apparatus and a test apparatus as well as to a coaxial cableand an assembled cable used for the apparatuses, capable of solving theabove-mentioned problems. This object may be achieved through thecombination of features described in independent claims of theinvention. Dependent claims thereof specify preferable embodiments ofthe invention.

That is, according to a first aspect of the invention, there is provideda current measuring apparatus for measuring current-under-measurementflowing between a first measuring terminal and a second measuringterminal, having a primary coil whose one end is electrically connectedwith the first measuring terminal and another end thereof iselectrically connected with the second measuring terminal, a secondarycoil that generates voltage representing the current-under-measurementcorresponding to the current-under-measurement flowing through theprimary coil and a coaxial cable having a signal line that connects oneend of the primary coil with the first measuring terminal and a shield,wherein the coaxial cable has the signal line, an insulating layer forcoating the signal line, first one of the shield having a tape-likeconductor wound around the insulating layer and second one of the shieldcomposed of a conductor provided around the first shield.

The current measuring apparatus may have a plurality of primary coils,the secondary coil that generates the voltage representing thecurrent-under-measurement corresponding to the current-under-measurementflowing through the plurality of primary coils and a plurality of thecoaxial cables, each corresponding to each one of the plurality ofprimary coils, having the signal line for electrically connecting theone end of the corresponding primary coil with the first measuringterminal and the shield.

The current measuring apparatus may further include a resistor forconnecting one end and another end of the secondary coil and may outputpotential of the one end of the secondary coil as a value representingthe current-under-measurement.

The current measuring apparatus may further include a core around whichthe primary coil and the secondary coil are wound, respectively.

According to a second aspect of the invention, there is provided a testapparatus for testing an electronic device, having a pattern generatingsection for generating an input pattern signal to be inputted to theelectronic device, a power supply section for supplying power to theelectronic device, a signal inputting section for supplying the inputpattern signal to the electronic device, a current measuring section formeasuring current-under-measurement flowing between a power terminal ofthe electronic device and the power supply section and a judging sectionfor judging whether or not the electronic device is defect-free based ona measured result of the current measuring section; the currentmeasuring section has a primary coil whose one end is electricallyconnected with the power terminal and another end thereof iselectrically connected with the power supply section, a secondary coilthat generates voltage representing the current-under-measurementcorresponding to the current-under-measurement flowing through theprimary coil, a coaxial cable having a signal line that electricallyconnects the one end of the primary coil with the first measuringterminal and a shield; and the coaxial cable has the signal line, aninsulating layer for coating the signal line, a first shield having atape-like conductor wound around the insulating layer and a secondshield composed of a conductor provided around the outer periphery ofthe first shield.

The power supply section may supply operating voltage to be received bythe electronic device by its power terminal to another end of theprimary coil. The power supply section may earth another end of theprimary coil. The current measuring section may measure thecurrent-under-measurement corresponding to changes of a value of theinput pattern signal.

The current measuring section may have a plurality of the primary coils,the secondary coil that generates the voltage representing thecurrent-under-measurement corresponding to the current-under-measurementflowing through the plurality of primary coils and a plurality of thecoaxial cables, each corresponding to each one of the plurality ofprimary coils, having the signal line for electrically connecting theone end of the corresponding primary coil with the first measuringterminal and the shield.

The electronic device may have a plurality of power terminal forreceiving potential set in advance, each of the power terminals may beelectrically connected with one end of either one of the primary coilsand the one end of each of the primary coils may be electricallyconnected with either one of the power terminals.

According to a third aspect of the invention, there is provided acoaxial cable, having a signal line, an insulating layer for coating thesignal line, a first shield having a tape-like conductor wound aroundthe insulating layer and a second shield composed of a conductorprovided around the outer periphery of the first shield.

A value of characteristic impedance between the signal line and thefirst shield may be 2.5Ω or less.

The first shield may have a tape-like insulator and a tape-likecomposite taping member composed of a tape-like conductor containing afirst region whose width is wider than the tape-like insulator and whichcontacts with the tape-like insulator in parallel and a second regionthat has a width set in advance from one edge of a tape width directionand that does not overlap with the tape-like insulator, and thecomposite taping member may be wound around the outer periphery of theinsulating layer so that at least part of the first region of thetape-like conductor overlaps with at least part of the second region ofpart of the tape-like conductor fore-wound around the insulating layer,so that the tape-like insulator does not overlap with the tape-likeinsulator fore-wound around the insulating layer in a radial directionof the coaxial cable and so that the side of the tape-like conductorcontacts with the insulating layer.

The tape-like conductor may contain a third region that has a presetwidth from an edge on the opposite side from an edge where the firstregion is provided in the tape width direction and that does not overlapwith the tape-like insulator, the composite taping member may be woundaround the outer periphery of the insulating layer so that at least partof the third region in the tape-like conductor overlaps with the outsideof the tape-like insulator fore-wound around the insulating layer andthe tape-like conductor may contact with the second shield by at leastpart of the third region.

According to a fourth aspect of the invention, there is provided anassembled cable having a plurality of coaxial cables havingsubstantially equal length, a fixing member for bundling the pluralityof coaxial cables in parallel so as to true up edges of the plurality ofcoaxial cables in an axial direction, a signal line connector having aplane vertical to the axial direction at each edge of the plurality ofcoaxial cables and provided with signal line connecting conductors forelectrically connecting respective signal lines of the plurality ofcoaxial cables exposed at the respective edges of the plurality ofcoaxial cables and a shield connector for electrically connectingrespective shields of the plurality of coaxial cables exposed in thevicinity of the respective edges of the plurality of coaxial cables.

It is noted that the summary of the invention described above does notnecessarily describe all necessary features of the invention. Theinvention may also be a sub-combination of the features described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing one exemplary configuration of a testapparatus 100 according to one embodiment of the invention.

FIG. 2 is a diagram showing one exemplary configuration of a currentmeasuring section 110 of the embodiment.

FIG. 3 is a flowchart showing one exemplary testing method of theembodiment.

FIG. 4 is a diagram showing another exemplary configuration of thecurrent measuring section 110 of the embodiment.

FIG. 5 is a drawing showing a structure of an assembled cable 500 of theembodiment.

FIGS. 6A through 6C are drawings showing exemplary wiring patterns of asignal line connecting conductor 560 of the embodiment. FIG. 6A shows afirst wiring pattern, FIG. 6B shows a second wiring pattern and FIG. 6Cshows a third wiring pattern, respectively.

FIG. 7 is a section view of a coaxial cable 204 of the embodiment seenfrom a direction vertical to an axial direction thereof.

FIG. 8 is a drawing showing a structure of the coaxial cable 204 of theembodiment.

FIG. 9 is a section view of the coaxial cable 204 of the embodiment inan axial section.

FIG. 10 is a drawing showing another exemplary structure of the coaxialcable 204 of the embodiment.

FIG. 11 is a table showing actually measured results of characteristicsof the coaxial cable 204 of the embodiment in a table format.

FIGS. 12A and 12B are graphs showing results of actually measured valueof characteristic impedances of the coaxial cable 204 of the embodiment.FIG. 12A shows the results of actually measured value of characteristicimpedances when a number of the coaxial cable 204 is one and FIG. 12Bshows the results when the number of coaxial cables 204 is five.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on preferred embodiments,which do not intend to limit the scope of the invention, but exemplifythe invention. All of the features and the combinations thereofdescribed in the embodiments are not necessarily essential to theinvention.

FIG. 1 is a diagram showing one exemplary configuration of a testapparatus 100 according to one embodiment of the invention. In thepresent embodiment, the test apparatus 100 is a test apparatus fortesting an electronic device 102 and has a pattern generating section104, a power supply section 108, a signal inputting section 106, acurrent measuring section 110 and a judging section 112.

The pattern generating section 104 generates an input pattern signal tobe inputted to the electronic device 102. The power supply section 108feeds power to the electronic device 102. In the present embodiment, thepower supply section 108 feeds the power to the electronic device 102via the current measuring section 110. The signal inputting section 106feeds the input pattern signal to the electronic device 102. Theelectronic device 102 may be provided in a test head for example.

The current measuring section 110 measures current-under-measurementflowing between a power terminal of the electronic device 102 and thepower supply section 108. In the present embodiment, the currentmeasuring section 110 measures the current-under-measurementcorresponding to changes of the value of the input pattern signal. Thecurrent measuring section 110 may measure transition of IDD currentcorresponding to the changes of the input pattern signal. The powersupply section 108 feeds the operating voltage VDD to a VDD powerterminal of the electronic device 102 in the present embodiment. Thetest apparatus 100 may perform an IDDT test on the electronic device102. Still more, the current measuring section 110 may measure changesof ground current corresponding to the changes of the input patternsignal. In this case, the power supply section 108 earths a VSS powerterminal of the electronic device 102. The current measuring section 110judges whether or not the electronic device 102 is defect-free based onthe measured result of the current measuring section 110. In the presentembodiment, the judging section 112 judges that the electronic device102 is defective when the measured result is greater than a value set inadvance.

Here, the electronic device refers to a parts that conducts apredetermined action corresponding to given current or voltage andincludes semiconductor parts composed of an active element such as an IC(Integrated Circuit) and an LSI (Large-Scale Integrated circuit). Stillmore, these parts may be what provided on a wafer, may be parts combinedand stored in one package or may be what mounted on a printed board torealize a predetermined function such as a bread board.

FIG. 2 is a diagram showing one exemplary configuration of the currentmeasuring section 110 of the embodiment. The current measuring section110 has a plurality of primary coils 22, a plurality of coaxial cables204, a first measuring terminal 208, a second measuring terminal 210, aresistor 206, a secondary coil 24, a core 20 and a current valuecalculating section 202. In the present embodiment, the currentmeasuring section 110 has n primary coils 22-1 through 22-n (n is apositive integer set in advance) and n coaxial cables 204-1 through204-n. The current measuring section 110 may measure thecurrent-under-measurement flowing between the first measuring terminal208 and the second measuring terminal 210.

One end of the plurality of primary coils 22-1 through 22-n iselectrically connected with the first measuring terminal 208 and anotherend thereof is electrically connected with the second measuring terminal210. For example, a terminal 26-k that is one end of the primary coil22-k (k is an integer satisfying 1≦k≦n) is electrically connected withthe first measuring terminal 208. Still more, a terminal 28-k that isanother end of the primary coil 22-k is electrically connected with thesecond measuring terminal 210.

Each of the plurality of coaxial cables 204-1 through 204n correspondsto each of the plurality of primary coils 22-1 through 22-n. Each of theplurality of coaxial cables 204-1 through 204n has a signal line thatelectrically connects one end of the corresponding primary coil 22 withthe first measuring terminal 208 and a shield. Preferably, the shield isearthed. Instead of that, the shield may be connected with a powersupply that outputs voltage set in advance and may be connected alsowith a VDD power supply that supplies operating voltage VDD of theelectronic device 102 for example. The shield may be also connected withthe second measuring terminal 210. In the present embodiment, the signalline of the coaxial cable 204-k electrically connects the terminal 26-kthat is one end of the primary coil 22-k with the first measuringterminal 208. Preferably, the plurality of coaxial cables 204-1 through204n has almost equal impedance characteristics, respectively.

The first measuring terminal 208 is electrically connected with thepower terminal of the electronic device 102 explained in connection withFIG. 1. Still more, the second measuring terminal 210 is electricallyconnected with the power supply section 108 explained in connection withFIG. 1. That is, the terminal 26-k is electrically connected with thepower terminal and the terminal 28-k is electrically connected with thepower supply section 108.

In the present embodiment, the terminal 26-k is electrically connectedwith the VDD power terminal of the electronic device 102. The powersupply section 108 feeds the operating voltage VDD, to be received bythe electronic device 102 by the VDD power terminal, to the terminal28-k. According to another embodiment, the terminal 26-k may beelectrically connected with a VSS power terminal of the electronicdevice 102. In this case, the power supply section 108 earths theterminal 28-k.

The resistor 206 electrically connects a terminal 30, i.e., one end ofthe secondary coil 24, with a terminal 32, i.e., another end thereof. Inthe present embodiment, the resistor 206 has impedance Z0 set inadvance. The secondary coil 24 generates voltage representing thecurrent-under-measurement corresponding to the current-under-measurementflowing through the plurality of primary coils 22-1 through 22-n. Theterminal 32 of the secondary coil 24 is earthed. In the presentembodiment, the secondary coil 24 supplies potential of the terminal 30,i.e., the voltage representing the current-under-measurement, to thecurrent value calculating section 202.

The core 20 is wound by the plurality of primary coils 22-1 through 22-nand the secondary coil 24, respectively. The core 20 is preferable to bea ferromagnetic core. The core 20 may be a ferrite core for example.

In the present embodiment, the core 20 is formed in the shape of a ring.That is, the core 20 is shaped like the ring having approximatelyrectangular outer and inner peripheries, in which the plurality ofprimary coils 22-1 through 22-n is wound around one long side of therectangle and the secondary coil 24 is wound around the other long side.According to another embodiment, the core 20 may be what the secondarycoil 24 is wound in lamination around the plurality of primary coils22-1 through 22-n.

The core 20 may be also a super-saturated core. It prevents thepotential of the terminal 30 from excessively increasing as the core 20saturates when a value of the current-under-measurement exceeds acurrent value set in advance. It then enables the current measuringsection 110 to efficiently measure the micro current-under-measurement.

The current value calculating section 202 calculates a valuerepresenting the current-under-measurement based on the potential of theterminal 30. The current measuring section 110 sends this value to thejudging section 112 explained in connection with FIG. 1. The currentmeasuring section 110 may output the potential of the terminal 30 as thevalue representing the current-under-measurement.

In the present embodiment, the plurality of coaxial cables 204-1 through204n connects the power terminal of the electronic device 102 with theplurality of primary coils 22-1 through 22-n in parallel. Therefore, thepresent embodiment allows the influence of the characteristic impedanceheld by each of the plurality of coaxial cables 204-1 through 204n to bereduced.

This parallel connection also reduces insertion impedance that is aneffect of the resistor 206 on the current-under-measurement of impedanceZ0. Therefore, a number of turns of the primary coil 22 may be two ormore in the present embodiment. In this case, the current measuringsection 110 can amplify the current-under-measurement with highamplification factor. Thereby, the current measuring section 110 canmeasure the micro current at high precision. Still more, the presentembodiment allows wiring parasitic inductance to be reduced byconnecting the power terminal of the electronic device 102 with theprimary coil 22 via the coaxial cables 204.

FIG. 3 is a flowchart showing one exemplary testing method performed bythe test apparatus 100 explained in connection with FIG. 1. This testmethod is what performed to test the electronic device.

According to the present embodiment, the test apparatus 100 generatesthe input pattern signal to be inputted to the electronic device 102explained in connection with FIG. 1 in a pattern generating step S102 atfirst. The pattern generating step S102 may be carried out by means ofthe pattern generating section 104 explained in connection with FIG. 1.Next, the input pattern signal is sent to the electronic device 102 in asignal inputting step S104. The signal inputting step S104 may becarried out by means of the signal inputting section 106 explained inconnection with FIG. 1.

Next, the voltage representing the current-under-measurement generatedin the secondary coil 24 explained in connection with FIG. 2 isoutputted as a measured result representing thecurrent-under-measurement in a current measuring step S106. Thesecondary coil 24 generates this voltage based on thecurrent-under-measurement flowing through the plurality of primary coils22-1 through 22-n explained in connection with FIG. 1. In the presentembodiment, the power supply section 108 explained in connection withFIG. 1 feeds the current-under-measurement to the electronic device 102.The current measuring step S106 may be carried out by means of thecurrent measuring section 110 explained in connection with FIG. 1.

Next, it is judged whether or not the electronic device 102 isdefect-free in a judging step S108 based on the measured result in thecurrent measuring step S106. In the present embodiment, the testapparatus 100 judges that the electronic device 102 is defective whenthe current value represented by the measured result is greater than thevalue set in advance in the judging step S108. The judging step S108 maybe carried out by means of the judging section 112 explained inconnection with FIG. 1. The test apparatus 100 may end the operationafter ending the judging step S108.

FIG. 4 is a diagram showing another exemplary configuration of thecurrent measuring section 110 of the embodiment. In this example, theelectronic device 102 is provided with a plurality of power terminalsthat receives potential set in advance. Each of the power terminals iselectrically connected with one end of either one primary coil and oneend of each primary coil is electrically connected with either one powerterminal.

In this example, the electronic device 102 has n VDD power terminals302-1 through 302-n. The current measuring section 110 has n firstmeasuring terminals 208-1 through 208-n. The first measuring terminal208-k is electrically connected with the VDD power terminal 302-k. Thecoaxial cable 204-k electrically connects the first measuring terminal208-k with the terminal 26-k of the primary coil 22-k.

The present embodiment allows the current flowing between the pluralityof VDD power terminals 302-1 through 302-n of the electronic device 102and the power supply section 108 explained in connection with FIG. 1 tobe measured. In another embodiment, the electronic device 102 may havemore VDD power terminals. In this case, one first measuring terminal 208is electrically connected with the plurality of VDD power terminals 302.According to a still other embodiment, one VDD power terminal 302 may beelectrically connected with a plurality of first measuring terminals208. The electronic device 102 may have a plurality of VSS powerterminals as the power terminals to be connected with the currentmeasuring section 110.

The plurality of terminals 26 may be electrically connected from eachother in the current measuring section 110 shown in FIGS. 2 and 4. Stillmore, instead of the plurality of primary coils 22 and the plurality ofcoaxial cables 204, the current measuring section 110 may have oneprimary coil 22 and one coaxial cable 204 connected with the primarycoil 22. Or, the current measuring section 110 may have one primary coil22 and a plurality of coaxial cables 204 connected with the primary coil22. In this case, each of the signal line of the plurality of coaxialcables 204 may electrically connect the terminal 26 of the primary coil22 with the first measuring terminal 208 common to the plurality ofcoaxial cables 204 or instead of that, may electrically connect theterminal 26 of the primary coil 22 with the first measuring terminal 208that is different from each other among the plurality of first measuringterminals 208.

FIG. 5 is a drawing showing a structure of an assembled cable 500 of theembodiment. The assembled cable 500 of the present embodiment isdesigned to reduce a value of characteristic impedance of the entireassembled cable 500 to what a value of characteristic impedance of thecoaxial cable is divided by a number of the coaxial cables by arrangingthe plurality of coaxial cables 204 in proximity and in parallel.

The assembled cable 500 has the plurality of coaxial cables 204, afixing member 540, a signal line connector 550 and a shield connector570. Each of the plurality of coaxial cables 204 corresponds to eitherone of the coaxial cables 204-1 through 204-n shown in FIG. 2 or 4. Theplurality of coaxial cables 204 has substantially equal length such as500 mm and is used in a state in which the signal line 520, i.e., aninternal conductor, is exposed by 3 mm, the insulating layer 525 by 0.8mm and the shield 530, i.e., an external conductor, by 1.0 mm at bothends of each coaxial cable 204. Here, each coaxial cable 204 is arrangedso as to suppress the value of characteristic impedance thereof toseveral Ω or less, or more preferably to 2.5Ω, in order to suppress thevalue of characteristic impedance of the assembled cable 500 to 1.0Ω orless, or more preferably to 0.5Ω or less. The fixing member 540 bundlesthe plurality of coaxial cables 204 in parallel so that each end of theplurality of coaxial cables 204 is aligned in an axial direction andfixes the plurality of coaxial cables 204 while arranging in parallel.More specifically, the fixing member 540 may be made of an adhesive tapeand may fix the plurality of coaxial cables 204 in the neighborhood ofthe both ends of the plurality of coaxial cables 204. Instead of that,the fixing member 540 may be made of a plastic tape and may fix theouter periphery of the plurality of coaxial cables 204 by melting. Or,the fixing member 540 may be made of a heat shrink tube and may fix theplurality of coaxial cables 204 by thermal shrinkage.

The signal line connector 550 has a plane vertical to the axialdirection at each end of the plurality of coaxial cables 204. The signalline connector 550 is provided with the signal line connecting conductor560 for electrically connecting each signal line 520 exposed at each endof the plurality of coaxial cables 204 and electrically conducts theplurality of signal lines 520 while disposing them in parallel. Thesignal line connector 550 may be a printed board provided verticallywith respect to the axial direction of the coaxial cable 204 forexample. In this case, the signal line connector 550 may have astructure of having a plurality of through holes into which the signallines 520 of the coaxial cables 204 are inserted and of connecting theplurality of through holes from each other by the signal line connectingconductors 560. Or instead of that, the signal line connector 550 may bea metallic belt molded by a die to realize as a plug whose whole planefunctions as the signal line connecting conductor 560.

The use of the signal line connector 550 and the electrical connectionof the respective signal lines 520 of the plurality of coaxial cables204 allow the plurality of signal lines 520 to be connected from eachother while equally keeping the length of the exposed signal lines 520and insulating layers 525, inductance, characteristic impedance andothers.

The shield connector 570 electrically connects each shield 530 exposedin the vicinity of each end of the plurality of coaxial cables 204. Theshield connector 570 may be copper foil of 1.0 mm in width and 20 μm inthickness for example.

The assembled cable 500 described above allows the value ofcharacteristic impedance of the entire assembled cable 500 to be reducedto what the value of characteristic impedance of the coaxial cable isdivided by the number of coaxial cables by arranging the plurality ofcoaxial cables 204 in parallel. That is, when five coaxial cables 204are arranged in parallel and the value of characteristic impedance ofeach coaxial cable 204 is 2Ω for example, the value of characteristicimpedance of the assembled cable 500 may be reduced to 0.4Ω. Still more,the use of the fixing member 540, the signal line connector 550 and theshield connector 570 allows the plurality of coaxial cables 204 to bebundled in a body while equally keeping the length and other thereof andallows the assembled cable 500 to be readily drawn around whilesuppressing dispersion of characteristics caused in each coaxial cable204 to the minimum.

FIGS. 6A through 6C are drawings showing exemplary wiring patterns ofthe signal line connecting conductor 560 of the embodiment. FIG. 6Ashows a first wiring pattern. The first wiring pattern is provided onthe signal line connector 550 to electrically connect the plurality of,e.g., five, signal lines 520 arranged in a row in the assembled cable500 in which the plurality of coaxial cables 204 are arrayed in a row.The first wiring pattern is suitable for realizing the assembled cable500 that can be readily bent in a direction vertical to the direction inwhich the coaxial cables 204 are arrayed.

In this case, the shield connector 570 connects the respective shields530 of the plurality of coaxial cables 204 by wrapping them.

FIG. 6B shows a second wiring pattern. The second wiring pattern isprovided on the signal line connector 550 to electrically connect therespective signal lines 520 while arraying the plurality of, e.g., five,coaxial cables 204 so that a section area occupied by the assembledcable 500 is minimized. In the second wiring pattern, wires are providedbetween a through hole into which the signal line 520 of the coaxialcable 204 disposed at the center is inserted and through holes intowhich the signal lines 520 of the respective coaxial cables 204 disposedaround that are inserted, respectively.

In this case, the shield connector 570 connects the shields 530 of thecoaxial cables 204 arrayed in a diagonal direction by wrapping them andthen by wrapping around the outer periphery of the respective shields530 of the entire coaxial cables 204.

FIG. 6C shows a third wiring pattern. The third wiring pattern isprovided to electrically connect respective signal lines 520 in a statein which a large number of, e.g., nine, coaxial cables 204 are arrayedin grid. Then, wires for electrically connecting through holes intowhich two or more signal lines 520 arrayed in each row in a rowdirection and wires for electrically connecting through holes into whichtwo or more signal lines 520 arrayed at least in one column in a columndirection are provided in the third wiring pattern.

In this case, the shield connector 570 connects the respective shields530 of the coaxial cables 204 arrayed in the center column direction bywrapping them at first and then by wrapping the outer periphery of therespective shields 530 of the entire coaxial cables 204.

FIG. 7 is a section view of the coaxial cable 204 of the embodiment seenfrom a direction vertical to the axial direction thereof. FIG. 8 is adrawing showing a structure of the coaxial cable 204 of the embodiment.FIG. 9 is a section view of the coaxial cable 204 of the embodiment seenin the axial section thereof. The coaxial cable 204 has the signal line520, an insulating layer 525 that coats the signal line 520, a firstshield 738 having a tape-like composite taping member 710 wound aroundthe outer periphery of the insulating layer 525, a second shield 740composed of a conductor provided around the outer periphery of the firstshield 738 and a sheath 750 provided around the outer periphery of thesecond shield 740.

The signal line 520 is a conductor such as tinned soft copper wire of0.52 mm for example. The insulating layer 525 has a tape-like insulator,or more specifically, a tape-like plastic member, wound around thesignal line 520. That is, the insulating layer 525 includes a firstinsulating layer 525 a in which a polyester naphthalate (PEN) tapehaving 1.2 μm of thickness and 3.5 of dielectric constant is woundaround the signal line 520 so as to overlap by half. The insulatinglayer 525 may also include a second insulating layer 525 b in which anadhesive tape-like plastic member such as a PEN tape having 1.2 μm ofthickness, hot-melt bond and 3.5 of dielectric constant is wound aroundthe outer periphery of the first insulating layer 525 a so as to overlapby half while putting the adhesive layer on the inside.

In this case, the first insulating layer 525 a is uniformly wound aroundthe conductor and the second insulating layer 525 b has the structure inwhich the tape-like insulator having the adhesive layer is wound aroundthe first insulating layer 525 a, so that winding tightening force isenhanced. Therefore, it allows the uniform and very thin insulatorhaving no dispersion of thickness and outer diameter to be realizedbecause the tape-like insulator is hardly loosened after it is wound andno irregularity of the outer diameter is caused due to the looseness. Asa result, the coaxial cable 204 can stably keep the value ofcharacteristic impedance as low as 2Ω for example.

The composite taping member 710 is made of the tape-like insulator 720laminated with the conductor 730. The insulator 720 may be a PET tape orthe like of 2.5 mm in width and 2.5 μm in thickness for example. Theconductor 730 may be a copper foil tape for example whose width is widerthan that of the insulator 720, e.g., 3.0 mm, and whose thickness is 9μm.

The composite taping member 710 of the embodiment is laminated so thatthe insulator 720 is positioned approximately at the center in a widthdirection of the conductor 730 and is wound around the outer peripheryof the insulating layer 525 while putting the conductor 730 on theinside and overlapping by half. More specifically, the conductor 730 hasa first region 732 whose width is wider than the insulator 720 and whichcontacts with the insulator 720 in parallel, a second region 734 whichhas a preset width from one edge in the tape width direction and whichdoes not overlap with the insulator 720 and a third region 736 which hasa preset width from another edge on the opposite side of an edge wherethe first region 732 is provided and which does not overlap with theinsulator 720. Then, the composite taping member 710 is wound around theouter periphery of the insulating layer 525 so that at least a part ofthe first region 732 of the conductor 730 overlaps with at least a partof the second region 734 that is a part of the conductor 730 fore-woundaround the insulating layer 525, so that the insulator 720 does notoverlap with part of the insulator 720 fore-wound around the insulatinglayer 525 in the radial direction of the coaxial cable 204 and so thatthe conductor 730 contacts with the insulating layer 525. The compositetaping member 710 may be also wound around the outer periphery of theinsulating layer 525 so that at least part of the third region 736 ofthe conductor 730 overlaps with the outside of the insulator 720fore-wound around the insulating layer 525.

In FIG. 9 for example, the composite taping member 710 is wound aroundthe outer periphery of the insulating layer 525 so that at least part ofthe first region 732 a overlaps with at least part of the second region734 b that is a part fore-wound around the insulating layer 525, so thatthe insulator 720 a does not overlap with the insulator 720 b fore-woundaround the insulating layer 525 in the radial direction of the coaxialcable 204 and so that at least part of the third region 736 a overlapswith the outside of the insulator 720 b fore-wound around the insulatinglayer 525. Then, because at least part of the conductor 730 is exposedto an outer face of the first shield 738, it contacts with the secondshield 740 at least at part of the third region 736. As a result, theconductor 730 and the second shield 740 function in a body as a shieldline and the outer diameter of the insulator part of the coaxial cable204 may be substantially assumed as the outer diameter of the insulatinglayer 525. Accordingly, the outer diameter of the signal line 520 may bebrought substantially closer to the outer diameter of the insulator partand then the characteristic impedance may be reduced.

The composite taping member 710 is composed of the copper foil of about9.0 sum in thickness and the PET of about 2.5 μm in thickness forexample as described above so that it withstands tension in windingaround the insulating layer 525 and so as to thin as much as possible.As a result, it becomes possible to suppress the composite taping member710 from being elongated or cut off and to prevent wrinkles and gapsfrom being generated in winding the composite taping member 710 aroundthe insulating layer 525. Then, because the first region 732 is woundaround the second region 734 that has been fore-wound as a result, thefirst shield 738 may closely adhere with the insulating layer 525 and acylindrical shield layer composed of the conductor 730 may be formed atthe part in contact with the insulating layer 525. Still more, becausethe composite taping member 710 formed as described above can maintainhigh cut-through resistance, the insulator may be readily peeled off.

The second shield 740 is formed by a plurality of conductive lines woundaround the outer periphery of the first shield 738 at preset windingintervals for example. That is, the second shield 740 is made of 35tinned soft copper lines of 0.05 mm wound in spiral at 4.5 mm of windingintervals for example. The sheath 750 is formed as an extrusion layer ofFEP resin of 100 μm in thickness for example. Based on the dimensionsexemplified above, the outer diameter of the coaxial cable 204 is 0.88mm.

Thus, the coaxial cable 204 described above realizes the transmissionpath whose characteristic impedance is low, whose dispersion ofcharacteristics is small and whose cut-through resistance is high byforming the insulating layer 525 by the very thin tape-like plasticmember and by forming the first shield 738 by the composite tapingmember 710 having the tape-like insulator 720 and the conductor 730.

FIG. 10 is a drawing showing another exemplary structure of the coaxialcable 204 of the embodiment. The coaxial cable 204 shown in FIG. 10 hasthe same structure with the composite taping member 710 within thecoaxial cable 204 shown in FIGS. 7 through 9, except of a point that ithas no third region 736, so that its explanation will be omitted hereexcept of the difference. The composite taping member 710 of thisexample is laminated so that the insulator 720 contacts with one edge ofthe conductor 730 in the tape width direction.

FIG. 11 is a table showing actually measured results of thecharacteristics of the coaxial cable 204 in a table formant based on thedimensions exemplified above. In a test of threshold voltage, AC voltage300 V was applied for 60 seconds between the signal line 520 and thefirst and second shields 738 and 740 to test whether or not theywithstand that. In a test of insulation resistance, the value ofinsulation resistance was measured after charging for one minute byapplying DC voltage 250V between the signal line 520 and the first andsecond shields 738 and 740.

FIGS. 12A and 12B are graphs showing actually measured results of thevalue of characteristic impedance of the coaxial cable 204 of theembodiment. FIG. 12A shows the actually measured results of the value ofcharacteristic impedance when a number of the coaxial cable 204 is one.In the actual measurement in FIG. 12A, the signal line 520 at one end ofthe coaxial cable 204 and the first and second shields 738 and 740 wereconnected with a SMA connector and the signal line 520 at the other endand the first and second shields 738 and 740 were connected in shortcircuit. FIG. 12B shows the result when the number of coaxial cables 204is five. In the actual measurement in FIG. 12B, the signal lines 520 atone end of the coaxial cables 204 were connected with each other throughthe signal line connector 550 and the shields 530 were connected witheach other through the shield connector 570 and were connected with theSMA connector. Still more, the signal lines 520 at the other end of thecoaxial cables 204 were connected with each other through the signalline connector 550, the shields 530 were connected with each otherthrough the shield connector 570 and the signal line connector 550 wasconnected with the shield connector 570 in short-circuit.

As shown in FIGS. 11 and 12A and 12B, the coaxial cable 204 based on thedimensions exemplified above realizes the coaxial cable having highthreshold voltage and having the value of characteristic impedance of2.0Ω to 2.5Ω by one cable and of 0.4Ω by five cables.

Although the invention has been described by way of the exemplaryembodiments, it should be understood that those skilled in the art mightmake many changes and substitutions without departing from the spiritand scope of the invention.

It is obvious from the definition of the appended claims that theembodiments with such modifications also belong to the scope of theinvention.

As it is apparent from the above description, the invention allows thehigh precision current measurement to be performed by transmitting thecurrent-under-measurement via the plurality of coaxial cables, byreducing the dispersion of the characteristic impedance of each coaxialcable and by realizing the low characteristic impedance.

1. A current measuring apparatus for measuring current-under-measurementflowing between a first measuring terminal and a second measuringterminal, comprising: a primary coil whose one end is electricallyconnected with said first measuring terminal and another end thereof iselectrically connected with said second measuring terminal; a secondarycoil that generates voltage representing said current-under-measurementcorresponding to said current-under-measurement flowing through saidprimary coil; and a coaxial cable having a signal line that electricallyconnects said one end of said primary coil with said first measuringterminal and a shield; wherein said coaxial cable has said signal line;an insulating layer for coating said signal line; first one of saidshield having a tape-like conductor wound around said insulating layer;second one of said shield composed of a conductor provided around anouter periphery of said first shield; a plurality of said primary coilswherein, said secondary coil generates the voltage representing saidcurrent-under measurement corresponding to saidcurrent-under-measurement flowing through said plurality of primarycoils; and a plurality of said coaxial cables, each corresponding toeach one of said plurality of primary coils, having the signal line forelectrically connecting said one end of said corresponding primary coilwith said first measuring terminal and the shield.
 2. The currentmeasuring apparatus as set forth in claim 1, further comprising: aresistor for connecting one end and another end of said secondary coil;wherein said current measuring apparatus outputs potential of said oneend of said secondary coil as a value representing saidcurrent-under-measurement.
 3. The current measuring apparatus as setforth in claim 1, further comprising a core around which said primarycoil and said secondary coil are wound, respectively.
 4. The currentmeasuring apparatus as set forth in claim 1, wherein thecurrent-under-measurement is divided to simultaneously flow into theplurality of said coaxial cables.